Method and device for detection and assessment of marijuana impairment

A device for identifying individuals impaired by a psychoactive substance other than alcohol, the device comprising:

• a display on which images are displayed monocularly to a subject being tested;
• to each eye separately with achromatic contrast between dark areas and light areas, the display presenting a pattern of fixed spatial frequency with contrast between the dark and light areas being temporally alternately modulated at a temporal frequency that ranges between 10 Hz and 60 Hz with a pattern of the contrast being such that the subject being tested can see a frequency doubling in the pattern thereby evaluating retinal function;
• the display being coupled to a processor that is programmed with an algorithm by which an operator can control the display to present the following procedure:
• decreasing the contrast of the pattern presented until a first contrast ratio/value is reached wherein the frequency doubling in the pattern is no longer reported as being seen by the test subject;
• further decreasing the contrast of the pattern until a second contrast ratio/value is below the test subject's threshold of detection of the second contrast ratio/value;
• increasing the contrast of the pattern until a third contrast ratio/value is reached where the frequency doubling in the grating pattern is first detectable;
• comparing the first contrast ratio/value and the third contrast ratio/value to a range of expected values of a normal population who have not consumed the psychoactive substance and have no pathology impacting the retinal visual functions tested;
• if the first contrast ratio/value and the third contrast ratio/value are within the range of expected values, then indicating that the test subject is not impaired;
• and
• if the first contrast ratio/value and the third contrast ratio/value are not within the range of expected values then indicating that the test subject is impaired.